Glyoxal, typically sold as a 40% aqueous solution, is an inexpensive chemical with a variety of industrial uses, most importantly for treatment of cellulosic textiles. The known bis(dialkyl acetal) derivatives of glyoxal of the formula: EQU (RO).sub.2 CHCH(OR).sub.2
are readily prepared in high yield (80-100%, depending on the nature of "R"). In contrast, the corresponding monoacetal derivatives of glyoxal of the formula: EQU (RO).sub.2 CHCHO
are much more difficult to prepare although the monoacetal derivatives of glyoxal are potentially versatile intermediates in organic synthesis. Current industrial-scale preparations of monoacetal derivatives have generally been avoided due to the difficulties inherent in previously-known routes which often require the use of hazardous reagents, lengthy reaction sequences, expensive reagents, and/or which result in complex product mixtures.
Different processes for making monoacetal derivatives of glyoxal have been reported. For example, ozonolysis of 3,3-dialkoxypropenes (acrolein dialkyl acetals) at low temperatures, followed by subsequent reduction with triphenylphosphine is reported to give a dialkoxy aldehyde, H. J. Bestmann and P. Erman, Chem. Ber., 116:3264 (1983). A multi-step process that uses comparatively expensive specialty chemicals (e.g., 3-ethoxyacrylonitrile and N-bromosuccinimide) is also reported to give a dialkoxy aldehyde, J. H. Babler, Synth. Commun., 17:77 (1987). Oxidation of commercially available, but expensive, 2,2-diethoxy-1-ethanol (glycolaldehyde diethyl acetal) to give the dialkoxy aldehyde is reported by D. Bernard, A. Doutheau, and J. Gore, Synth. Commun. 17:1807 (1987).
Partial acetalization of aqueous glyoxal is reported by A. Stambouli et al., Bull. Soc. Chim. France, 95 (1988). Although this reported one-step method yields 2,2-dialkoxyethanals (i.e., monoacetal derivatives of glyoxal), careful monitoring of the reaction is required to avoid acetalization of both carbonyl groups of glyoxal; the yield of monoacetal product is only moderate (50-70%). A reported improvement for this type of acetalization reacts various 1,3-propanediol reagents with glyoxal in 1,2-dichloroethane at high temperatures, but the monoacetal derivatives obtained in this manner are isolated only after careful vacuum distillation and frequently several repetitions of the high-temperature process may be necessary to obtain an acceptable yield. See European Patent 316,672 (Nov. 4, 1988).
Finally, a single monoacetal glyoxal derivative, (CH.sub.3 O).sub.2 CHCHCl(OCH.sub.3), has been reported by Bou et al., Tetrahedron, 37:1441-1449 (1981). This derivative was obtained as a minor component of a reaction mixture which resulted in the formation of the sought-after dichloro compound (CH.sub.3 O)ClCHCHCl(OCH.sub.3) as the major product.
As noted above, monoacetal derivatives of glyoxal have potential use in a variety of synthetic processes. For example, the compound (RO).sub.2 CHCHO is reportedly used in the manufacture of vitamin A. See, European Patents 246,646 (May 21, 1987) and 316,672 (Nov. 4, 1988). Alpha-halo ethers derived from glyoxal, due to the high reactivity of the carbon-chlorine bond in such compounds in nucleophilic substitution reactions, are attractive intermediates in the manufacture of several known industrial compounds, as well as prospective intermediates in the manufacture of various known or novel specialty organic chemicals.
Another example of the synthetic utility of 1-chloro-1,2,2-trialkoxyethanes involves their reaction with primary amines. For example, reacting these copounds with benzylamine gives the intermediate (RO).sub.2 CHCH.dbd.NCH.sub.2 Ph, in high yield. This intermediate may be readily converted to isoquinoline, a heterocyclic compound with extensive industrial uses, by treatment with aqueous acid as reported by E. Schlittler and J. Muller, Helv. Chim. Acta., 31:914 (1948). Glyoxal monoacetal derivatives may also be used to prepare, various alpha, beta-unsaturated aldehydes, unsymmetrically-substituted 1,3-dienes, and numerous other compounds of the general structure W.dbd.CH--CH.dbd.Z (W.noteq.Z).
In view of the broad application of monoacetal derivatives of glyoxal to synthetic methodology, a need exists for a facile method of preparing these derivatives using inexpensive, readily-available reagents and solvents.